I'd argue that the key word here is "trauma"; I think _adversity_ can make you stronger (more disciplined, and more focused), but I think that Dr. Bernstein is using the word "trauma" in its technical, medical, sense, i.e. "Psychological trauma is caused by an adverse experience, or series of experiences, that result in an injury that changes the way the brain functions, impairing neurophysiological, psychological, and cognitive functioning." [0]
There is large heterogeneity in the reaction of individuals to the sane exact experience, and sometimes what initially appears damaging ends up doing the opposite.
There is a circular definition here. If we define trauma in terms of harmful outcomes, it's bad by definition, but that's arguing semantics and not psychology. The slipperiness comes in when we switch definitions mid-paragraph.
You'll also see virtually everyone 300 years ago was exposed to things which would be considered traumatic today. It's how we evolved.
We've got a bad theory of trauma and resilience.